This is a Phase II study to look at the effects of the investigational drug DMP 543 which has potential potent effects on platelet aggregation. This protocol consists of two parts. Part A is a dose ranging study of IIb/IIIa antagonist. Based on the findings in Part A, a second part B study will be performed using the optimum doses identified. Endpoints include tolerability and safety and also effectiveness in inhibiting platelets as assessed by platelet aggregation studies.